It is well known to use a spinstand to test various components of a hard disk assembly, such as in particular the read/write heads and the disk media. Such tests can be carried out in a manufacturing production environment, where typically every head and a proportion of disks are tested prior to being assembled into a hard disk assembly to ensure that they perform to the required standard. Testing using a spinstand can also be carried out in a research and development setting.
A spinstand typically comprises a deck, for example of granite, which is generally isolated from external sources of vibration in some way to avoid these affecting the accuracy of the test results. A spindle is attached to the deck for holding and rotating the disk. This will typically be an air bearing spindle with an integrated DC brushless motor.
The spinstand also has a so-called “test nest” which is adapted to hold the read/write head during testing and to make electrical connections to the head. The test nest is mounted on a puck that is movable on the surface of the deck, typically on an air bearing, so as to be capable of moving the head to a desired location under the surface of the disk. The puck is typically positioned by a highly accurate x-y positional stage, also supported by air bearings and having linear encoders to allow the position of the puck to be highly accurately determined. It may also be possible to lock down the puck and/or elements of the x-y stage to the granite by application of a vacuum in order to prevent movement of the puck when in a desired position. The puck generally has some arrangement for loading/unloading the head to/from the test surface of the disk to allow the head to read from and/or write to a track of test data on the test surface of the disk. The puck also generally has some arrangement, such as a nanopositioner disposed between the puck and the test nest, for making very fine positional changes of the head relative to the test track.
When testing a head with a spinstand it is important that the head is positioned with great accuracy relative to the disk. It is therefore important that the head be loaded to the test nest with great positional accuracy. It is also important that the positioning of successively tested heads is consistently repeatable. In particular, it is important to control the x-y position of the head (i.e. the position of the head in the x-y plane parallel to the disk surface) and the theta position of the head (i.e. the rotational position of the head in the x-y plane). Discrepancies in the x-y positioning of the head affects the ability of the apparatus to position the head over a test track of data on the disk. Discrepancies in the theta positioning affects the skew of the head when positioned over a test track on the disk, which in turn affects the characterisation of the head.
When testing a read/write head with a spinstand in a production environment the test apparatus typically comprises a spinstand in combination with a receiving stage where heads are loaded and unloaded to the apparatus, and automation for moving heads between various areas in the spinstand and the receiving stage. The heads to be tested are usually delivered to the receiving stage in the form of head gimbal assemblies (HGAs) arranged in a tray. The tray will hold for example 10 or 20 HGAs arranged in a row. The automation includes a highly accurate linear actuator which extends above the relevant parts of the spinstand and has a pick device for picking up and subsequently placing down HGAs along its path.
To load a HGA to the apparatus, the linear actuator moves the pick device to above the tray which is received in the receiving stage and the pick device picks up an individual HGA. The pick device then moves the head to a so-called precisor. The precisor is normally mounted to the deck and is arranged to “precise” (i.e. finely position) the HGA in x, y and theta positions. Since the precisor and the spindle are both registered to each other via the deck, once the HGA is finely positioned by the precisor, its position relative to the spindle and thereby to the disk are set. Once the head has been précised, the pick device picks up the HGA from the precisor and transfers it to the test nest of the puck. The test nest usually has a collet arrangement for clasping the boss hole of the base plate of the HGA in order to hold the HGA in position. The head is then loaded to the disk for testing.
A drawback of this automation is the vibration that it generates. It is important to isolate the spinstand from vibration as much as possible as vibration can affect the accuracy of the test results. It has therefore been proposed to isolate the automation from the deck of the spinstand. However, isolating the automation from the spinstand means that the automation cannot place the HGA on the precisor with the same accuracy. Also, when transferring the HGA from the precisor to the test nest with the automation, the accuracy of the fine positioning achieved by the precisor is to some extent lost when the automation is isolated from the deck.
Another disadvantage of the automation described above is that the highly accurate linear actuator used to move the HGA around the apparatus is expensive. For this reason, it is not generally used in a research and development setting, where speed of swapping heads is generally of less importance and so does not justify the expense. Accordingly, in a non-production spinstand the HGAs are usually manually precised and manually loaded to the spinstand. This is done by first mounting the HGA in a cartridge or block (typically a block of stainless steel) away from the spinstand. In so doing, the operator will align the HGA to the cartridge with great precision, for example with the aid of a microscope. The cartridge is then attached to the test nest of the spinstand in such a way that the cartridge is keyed with the test nest. Thus the HGA is mounted to the puck in such a way that the position and orientation of the head is known. The disadvantage of this technique is that the alignment process is labour intensive and time consuming, and requires a skilled operator on hand to perform correctly.
A further drawback of this technique is that the production spinstand and the research and development spinstand have less parts in common due to the different way in which the HGA is attached to the test nest. It is generally desirable to have as many parts in common as possible between a spinstand intended for production testing and research and development testing.